Well you could always set the 3, or however many partitions you want or have like this:
If there is only one user on the system you could always mount them under your username:
Replacing username with your own of course. Also, the partition names can be whatever you want, they don't need to be named with what I put. If you're going to do everything over again, then do this while in gparted during install...
If you're going to do this after install, then you'd need to mount them or symlink once it is all said and done.
I usually make one data partition, and have different folder names for each. That way they are all seperated from your /home partition should you desire to replace your Mint OS or distribution altogether.
You can follow Fred's instructions here for further information on mounting partitions. viewtopic.php?f=42&t=22093